Baby Sister
by JorJorLaforge
Summary: OC, lives at the Institute, post City of Glass. It's a Jace/OC ship : angsty and romantic, yay! M for later chapters, hopefully. Also, some language
1. Chapter 1

**A/N:: Hello, there, fellow Mortal Instrument fans. Okay, so I have only read to City of Glass, and I am waiting for the last book to come out before finishing the series, don't ask why, I just am, so please, don't ruin anything for me, if you have read City of Fallen Angels, and the City of Lost Souls, I don't want to know what happens. Also, this is an Original Character fanfiction, so go easy. Anyway, reviews are always very welcome Thanks 3 **

In front of her eyes her sister was bleeding, the sickness she had always been afraid of, taking hold of her body and breaking it. The frail body of the 6 year old had nothing left to vomit up, only blood, which slowly streamed out of her mouth, nose, and eyes. Cradling her in her arms, Jordyn felt nothing but the breaking of her heart. It was a pain so intense she couldn't function. She had collapsed to her knees and gathered up her sister, holding her as if it could stop what was happening.

Before she could register it, Jace had ripped her away from her sister, and driven a seraph blade through the chest of the small, broken body. Screaming in rage, Jordyn reached up to tear at his face, to strike him, but all of her energy was gone, all she could do was scream as hot tears streamed down her face.

A flash of bright white and she was sitting up in bed. There were tears on her face and pillow, sweat down her back and she had kicked her covers into a ball at the end of her bed. The image of her Katie with a blade in her breastbone was seared into her mind's eye, and every time she blinked, it was there, like a camera's flash, or a lightning strike. Around her, her room was boringly the same as when she had gone to sleep a few hours before. Wearily, she dragged herself to a standing position and made her way into the bathroom, untying her hair and letting it fall in waves around her shoulders.

It had been a year since that day on Valentine's boat, floating in the East River. Exactly one year since Agramon had forced her to witness her sister's body betray itself. Again. Jordyn remembered the overwhelming joy that had swelled in her chest as she had seen her sister walking towards her, arms outstretched for a hug. Knowing it was a lie, but hoping without hope that her sister had recovered. Until she had started retching, and bleeding, breaking, and dying…. Again.

She could never remember what had happened after she tried to tear Jace apart with her bare hands. Only blacking out and waking up back in the Institute, hearing about how Clary could make more powerful Marks than anyone, and Simon could walk in the sunshine. When she had tried to apologize to Jace, he had shrugged her away, muttering something about knowing what Agramon could do. Since that day, she had retreated into herself, focusing on things that numbed the constant ache in her heart, and forced the lump in her throat to go away. The threat of crying wasn't as constant as it had been at first. She would shut herself in her room, music blaring, so no one would hear the sobs. It had been selfish, she knew. She wasn't the only one with a reason to be sad. Especially in the following month, with the Battle of Alicante, the truth about Jace and Clary, Valentine's death, and the whole upturn of the system; Downworlders and Shadowhunters working together. The thought was still strange, though not unwelcome.

Standing under the hot stream of water from her showerhead, the painful images started to slowly leave her vision. She turned the knob to the right, cooling the temperature to just above freezing. As the water stabbed her skin all over, she managed to draw in a shaky breath and force all thoughts of that day from her mind. She cleared her mind of everything except what weapons she was going to use to kill demons today. Reaching out, she jerked the handle all the way off, and stepped out of the shower. Wrapping a towel around her body, and another around her hair, she opened the door that connected her bathroom and her bedroom, and was surprised to find Jace standing next to her bed, looking out her window, looking almost like the old Jace. Silent, moody, unreachable.

He had changed since finding out he was Stephen Herondale's son. Since he knew he could have Clary. It had been nice to see him happy. A nice change from the tortured look in his eyes since he had met her, since Valentine had started twisting his web of lies. He tore his gaze away from the New York skyline to look at her, one eyebrow shooting up on his angelic face. Smiling at this, Jordyn crossed to her closet and started rummaging for something to wear.

"What do you want, Jace?" She asked over her shoulder, not unkindly. When he didn't reply, she emerged from her closet to look at him. His face looked worried as he said, "I heard you screaming again."

"Oh.." Not knowing how to reply, Jordyn continued her search for clothes. Finally she settled for a pair of jeans and the sweatshirt she'd gotten at Disneyworld two years ago. It was one of a pair. The matching sweatshirt was small, made for a child, and had been thrown out after it got covered in blood and bile a year ago. Swallowing and pushing away more thoughts of her sister, Jordyn tossed the sweatshirt back into the pile of clothes and instead grabbed a plain, long-sleeved, midnight blue v-neck. "Sorry if I woke you," she mumbled after a moment, still staring at the clothes in her hands, not daring to look at Jace.

"You didn't." His voice was soft, and she could hear the sorrow in his voice. She knew he was thinking of Max. "You usually do, but I was already awake this time."

Looking up at him, her mouth fumbled to form an apology. The nightmares had become more frequent lately, but she didn't know anyone else had known, or noticed. "Jace, I'm sorry…."

"No, it's…. don't be… but, you said my name this time. Usually you just scream 'Katie,' or 'Agramon,' or just.. scream. But… you said 'Jace.' You've never said my name before."

"Because I usually wake up before the part where I try to kill you." Her voice shook, but she held his gaze. When he started to reply, she cut him off. "I'm going to get dressed now," she said, and whirled back to the bathroom, pausing only to grab underwear and a bra out of her dresser. When the door slammed behind her, she hastily fumbled to dress herself. She tore the towel off from around her hair, and raked a brush through it once. She didn't care how she looked, because a long time ago, she had resigned herself to knowing she would never be as striking as Clary. Her hair was long, black, and boring. It wasn't wavy and straight like Izzy's, and it wasn't bold and on fire like Clary's. She wasn't Amazonian tall, and she wasn't abnormally short. Everything about her was average. Her eyes were brown, her skin the color of melted caramel, lined with the scars of leftover Marks. If she hadn't been born a Shadowhunter, there would have been nothing outstanding about her at all. Nothing to give her life a purpose. She hastily applied mascara and eyeliner and fishtailed her hair over her right shoulder. In her skinny jeans and baggy sweatshirt, she looked as boring as ever. Sucking in a deep breath, she returned to her bedroom to find Jace sitting on her bed, looking as unconcerned as ever. She wondered why she hadn't heard him turn her stereo on, but it was on. Her favorite song pumping out of the speakers, slow, sweet, the singers voice pouring out in notes that broke her heart and put it back together again.

"Hey, Jace." She said. "Sorry to be so dramatic."

"No, it's not a problem." His voice was so understanding that it made her want to scream. She liked to think she was the only one who felt her pain. "Every night, you see me stab a seraph blade through your sister's heart. I'd be dramatic too."

Tears sparked at her eyes, "Jace…"

"When I'm not seeing my father run me through with a knife, I'm seeing Sebastian murder Max…." his voice wavered, and for some reason this made her mad. Anger flared up in her chest. He never used to be so open, so vulnerable. She could always depend on him to be steady, and now he bared his emotions to everyone. It was Clary's fault. She had made him soft.

"I don't care," she spat through gritted teeth. "Jace, I don't care."

Instead of looking angry or hurt, he smiled. It was a sad smile. "Yes you do, Jordyn. You care too much."

"No I don't!" she snapped at him, hating that the prickle of tears behind her eyes was worse than ever. In a second he was standing in front of her, his face lowered to be right in front of hers, his eyes locked on hers. "Lie to me. Don't lie to yourself." His voice was full of concern and caring and not the harsh sarcasm she was used to, and she hated him for it. But before she could reply, Clary burst into the room, full of life, energy, a swirling tornado of chaos that she brought with her everywhere. Suddenly all emotion disappeared, and Jordyn just rolled her eyes.

"Jace?" Clary said, sounding concerned. He straightened up and smiled at her, the same sickening smile that exploded onto his face every time he saw her. It made Jordyn's stomach flip with nausea, and she walked away from the now embracing couple to scoop her phone off of her night stand. No missed calls, no new texts. It was the same blank screen as always, the background set to a default color, because she had hated having to look at the smiling face of a sister who didn't exist anymore. She flung it back down on the bed and sat down to pull her sneakers on. She didn't look up when Jace and Clary started talking to her, saying her name, asking her if she was alright.

Once she had laced up the dark read Converse, she stood up straight and fast, causing Clary, who had been leaning over her, to stumble backwards. Fighting back a satisfied smile, Jordyn scooped up her phone off the bed and pocketed it, then reached for her wallet, took out a few bills and stuffed those into her pocket. Ignoring more questions and looks from Clary, she mumbled that she was going out and headed for the door. Frustratingly, and predictably, Jace got there first. "No, we need to talk."

"About what?" she cried, exasperated. "Can't you tell I don't _want_ to talk to you two?" She tried to shove Jace, but he didn't move. She pushed harder but he still stood there, infuriatingly calm. She bit back the urge to shout at him and instead whirled around to face Clary. "Get him out of my way!" she snapped, her tone harsh. Clary looked at her, alarmed, obviously wondering why someone would ever be displeased with someone as _perfect_ as herself. Sickened, Jordyn turned around and in one swift motion, ducked under Jace's arm, and out of the door before he could react. She was in the elevator before they had reached the end of her hall, and headed out onto the streets of New York City, headphones plugged in, hoping to pick a fight with someone strong enough to maybe make her tired enough to get some sleep tonight.


	2. Chapter 2

Walking through the entrance to Pandemonium, Jordyn scanned the crowd of angsty teenagers dancing to some new unintelligible rap song. She knew this was where Jace and Clary had first clapped star-crossed eyes on each other, but it was also a popular place for demon activity, and she was just raring for a good fight. The _Mendelin_ rune on her shoulder was doing it's job effectively and she slunk through the writhing bodies fueled by hormones without being detected. She wanted to find something big enough and bad enough to give her a good run for her money.

Jordyn had always been careful about the demons she fought. She never went hunting on her own, and she never went looking for something bigger than her. Lately, that's all she seemed to do. She was in the institute only to get a few hours of nightmare-riddled sleep, and check to see if there was anything important that they needed her help with. Otherwise, she was walking the streets of this big city, slinking through Downworld and cutting down rogue demons wherever she could find them. Valentine was dead, but the demons were still here, still behaving as filthy and vile as before.

"KATIE!" Someone called out to their friend, and Jordyn whipped around. Two blonde, pale, sixteen year old girls ran to embrace one another, and it made her blood boil. Katie, her little sister, still dead. She would never be a teenager. And the stupid thing was that there was absolutely _nothing_ Jordyn could have done to stop it. Her own body betrayed her. There was no demon, no warlock, no vampire to blame for her sickness. Just bad genetics, unfixable by any stupid spell. Jordyn's parents had died when Katie was two, and the sisters had come to live in the Institute ever since. Even the useless Silent Brothers couldn't do anything for the innocent little girl. Frustrated, Jordyn realized there were no demons here in this idiotic club, and the only thing she smelled was the stink of hormones and alcohol that had been smuggled past the bouncers somehow.

Out in the street again, Jordyn turned and headed farther away from the Institute. She could picture Jace and Clary working together to figure out what her problem was, why she was such a bitch. If she was honest, Jordyn had to admit that there really was nothing wrong with Clary. She was bloody-well perfect, nearly, and everyone else loved her. Even damn Izzy like her. Alec didn't even hate her anymore, and Jordyn was pretty sure that she wasn't Church's favorite anymore. Traitorous freaking cat. Stomping past taxis and diners, she thought about Jace, and how much she had liked and wanted him when she'd first moved to New York. He was beautiful and mysterious, and moody. Unreachable, and troubled, and irresistible. He had never liked her back, never shown any inkling of mutual feelings, and Jordyn wasn't one to embarrass herself with words and unrequited declarations of love. They were a stupid waste of her time. She felt that way about most things, to be honest, but feelings especially were a waste of time. They harbored nothing but pain and disappointment, except for anger, and determination, because with a little anger (and she had a lot) and some determination, you were able to get shit down a demon was easier if you were angry about a lot of other things. It had always been easy before, but anger helped. It fueled Jordyn's fire, and when she walked by an alley and smelled the reek of a demon den, her fire roared up inside and she pulled a Seraph blade out of the holster on her waist.

It was about 4am when she finally got back to the Institute. She was covered in blood and ichor with an obscene grin on her was peeling off the gear on her arms on the way to the training room, hoping to work off the adrenaline still pumping through her veins. When she pushed the door open, there was no one else in there so she found her favorite set of throwing knives and went to work on one of the many-abused targets.

An hour later, her arm was too tired and sore to throw any more, so she pulled them out from the center circle for the last time that night. As far as she was concerned, it had been a damn good night, and she was hopeful that she might get some actual rest, when she turned to see Jace standing in the door of the training room.

"Shit!" she cried out, almost dropping a knife on her foot. "What the hell are you doing, you scared the hell out of me!"

"You're aim's a little off," was his answer.

"How long have you been standing there?"

"I don't know, since about five minutes after I heard you come back."

"For fuck's sake, Jace, you could have said something." Jordyn was putting the knives back in their place as he mumbled something. "What?"

"I said that I didn't want to distract you. Plus, I wanted to see how long you could throw knives at a board before you gave up."

"It's like a therapy, Jace, leave it alone."

"Where were you?"

"Out, stupid."

"Obviously, but where?"

"Demon den. I don't know how many, but I killed them."

He didn't respond so she pushed past him into the hall and started towards her room.

"You need to talk to us," he said, grabbing her arm and stopping her. "You need to talk to somebody."

"Who says?" He didn't answer and she glared at him. His eyes burned their bright gold and she wanted to slap him for being so perfect. "Jace, I don't know if you feel responsible or whatever, but it's not your fault. What I'm doing, nothing is your fault, you know? And I don't want you to feel like it's up to you to 'fix me' or whatever, because I'm totally fine."

"You're not fine," he said, but loosened his grip on her wrist. "You're the furthest from fine you've ever been."

"Well, there's nothing you can do about it. Just leave me alone, okay?"

"You really want me to leave you alone?"

"For a while... yeah." He was staring right at her, and she thought the conversation was over, so she turned to walk away, but then he said; "What happened? You were my best friend, besides Alec. Why... it's like you hate me now?"

A sigh escaped her lips, and Jordyn couldn't think of a good answer. "I don't know Jace. No, I clearly do not hate you. I could never hate you. Not in a million years."

"Then why won't you talk to me?!" He raised his voice. He was angry, really angry, and it was her fault, all her stupid, pig-headed fault, so Jordyn just walked away. She couldn't answer him because it was humiliating and unnecessary and she wished again that he would just go back to being who he was, the silent, moody boy that she secretly, in her heart of hearts, always longed for, but it was understood that they didn't talk this mushy shit over, that it just was and would always be unspoken. Now he was demanding her to explain herself to him and while she didn't hate him, she truly never could, she was so frustrated with him for expecting her to change as he has, but she couldn't because, well, because she just wasn't going to, no matter what. She stomped into her room, locked the door, and flopped onto her bed, still in her blood-caked gear, and the exhaustion that she had hoped would carry her into unconsciousness was gone again, so she lay staring at her ceiling until the sun was fully up, burning through her window and mocking her in its happiness.


End file.
